Hydraulic radial piston motor

ABSTRACT

A hydraulic motor having radial pistons, and comprising a cam, a distributor, and a cylinder block whose cylinders are connected to communication orifices situated in a communication face of the cylinder block. The distributor has a distribution face in which distribution orifices open out that are suitable for communicating with the communication orifices while the cylinder block and the distributor are turning relative to each other. The cam is provided with a plurality of lobes, each of which has two ramps ( 50 ), each of which has a convex portion ( 51 ) and a concave portion ( 52 ). The edge of each distribution orifice has a leading portion (B 1 ) via which communication between the distribution orifice and the communication orifices opens, and a trailing portion (B 2 ) via which said communication closes. Each leading portion (B 1 ) and each trailing portion (B 2 ) of the edges of at least certain distribution orifices ( 21 A,  23 A) has an edge arrangement ( 53 A;  53 B) provided with at least one notch ( 54 A;  54 B), said edge arrangements of a distribution orifice being different depending on whether they are in angular correspondence with the convex region ( 51 ) or with the concave region ( 52 ) of the ramp of the cam.

The present invention relates to a hydraulic motor having radialpistons, and comprising a cam and a cylinder block that are suitable forturning relative to each other about an axis of rotation. The cylinderblock has radial cylinders connected via cylinder ducts to communicationorifices situated in a communication face of the cylinder block that isperpendicular to the axis of rotation. Pistons mounted to slide in thecylinders are suitable for co-operating with the cam, which cam isprovided with a plurality of lobes, each of which has two ramps, each ofwhich has a convex region and a concave region. The motor furthercomprises a fluid distributor having a distribution face that isperpendicular to the axis of rotation and that is suitable for being inabutment against the communication face of the cylinder block, saiddistribution face being provided with distribution orifices comprisingorifices suitable for being connected to a fluid feed and orificessuitable for being connected to a fluid discharge. The fluid distributoris constrained to rotate with the cam, so that there is one ramp of thecam that corresponds to each distribution orifice (i.e. eachdistribution orifice is situated in angular correspondence with arespective ramp of the cam), said distribution orifices being suitablefor communicating one after another with the communication orificeswhile the cylinder block and the distributor are turning relative toeach other, the edge of each distribution orifice having a leadingportion via which communication between the distribution orifice and thecommunication orifices opens while the cylinder block and thedistributor are turning relative to each other in a given direction ofrelative rotation, and a trailing portion via which communicationbetween the distribution orifice and the communication orifices closeswhile the cylinder block and the distributor are turning relative toeach other in the same direction of relative rotation.

For a motor of this type, operating at full cubic capacity, eachcommunication orifice successively comes to face a distribution orificeconnected to the fluid feed and comes to face a distribution orificeconnected to the fluid discharge. The communication orifice in questionbeing coupled to the distribution orifice that is connected to the feedcauses the piston contained in the cylinder connected to saidcommunication orifice to be pushed radially outwards, while the samecommunication orifice being coupled to a distribution orifice that isconnected to the fluid discharge makes it possible to cause said pistonto return-into its cylinder, towards the axis of the motor. Thus, eachpiston co-operates successively with the various portions of the lobesof the cam so as to enable the cylinder block and the cam to rotaterelative to each other.

The spacing between the distribution orifices and the spacing being thecommunication orifices are such that a communication orifice is notsimultaneously connected to two distribution orifices respectivelyconnected to the fluid feed and to the fluid discharge.

While the cylinder block and the distributor are rotating relative toeach other, the working chambers of the cylinders, i.e. the portions ofsaid cylinders that are defined under the pistons, are placedalternately at high pressure and at low pressure. Therefore in saidworking chambers, changes in pressure generally take place at a veryfast rate. Such changes in pressure subject the pistons to proportionalforces, and said forces are transmitted by the pistons to the cam.

As a result, the components of the motor, in particular its casing, aresubjected to the variation in load, which causes noise-generatingvibration, the intensity of the noise generated depending mainly on thespeed of the increases and decreases in pressure in the workingchambers.

In order for the motor to operate correctly, the difference in pressurebetween the fluid feed and the fluid discharge is large. When a pistoncontributing to the drive torque reaches the end of its stroke towardsits position that is furthest from the axis of the motor (top deadcenter), due to the communication orifice of its cylinder beingconnected to a distribution orifice connected to the fluid feed, thesame communication orifice is isolated from said distribution orifice,and is then connected to another distribution orifice which is connectedto the fluid discharge. This results in a phenomenon of pressurereduction in the cylinder of the piston in question, the fluid presentat a high pressure in the cylinder being suddenly put into communicationwith a significantly lower pressure, which is the pressure of the fluiddischarge. Conversely, when the piston reaches the bottom dead center ofits stroke (its position that is closest to the axis of the motor), itscylinder is isolated from the fluid discharge, and is then connected tothe fluid feed so as to enable the piston to travel over a centripetalstroke again. At this instant, the fluid contained in the cylinder goesfrom a low pressure to a pressure that is much higher, which is thepressure of the fluid feed. A phenomenon of pressure reduction alsogenerally takes place, from the fluid feed, towards the cylinder. In thepreceding case, the pressure reduction takes place from the cylindertowards the fluid discharge.

In both cases, the pressure reductions that take place generate joltingor juddering sensations, and noises such as knocking.

The more the quality of such motors is improved, and the greater theextent to which leaks are reduced in such motors, the more perceptiblesuch phenomena become. In old motors, the leaks prevailing in them madeit possible to avoid variations in pressure that were too sudden betweenthe various enclosures.

An object of the present invention is to limit the phenomena of pressurereduction and the resulting jolting effects, while tending to enable themotor to operate substantially smoothly.

This object is achieved by the fact that each leading portion and eachtrailing portion of the edges of at least certain distribution orificeshas an edge arrangement provided with at least one notch, said edgearrangements of a distribution orifice being different, the edgearrangement of a distribution orifice which is disposed in angularcorrespondence with the convex region of the ramp of the camcorresponding to the distribution orifice in question being suitable forallowing a pressure-compensating volume of fluid to pass through betweena communication orifice and the distribution orifice that is smallerthan the pressure-compensating volume of fluid that is allowed to passby the edge arrangement of the same distribution orifice that isdisposed in angular correspondence with the concave region of said ramp.

These compensation volumes of fluid are volumes of fluid capable oftransiting via the notches in said edge arrangements so long as thecommunication between the distribution orifice and a communicationorifice is established solely via the notch or notches in the edgearrangement in question.

In order to remove the above-mentioned jolting and noise phenomena, orat least in order to attenuate them considerably, the invention proposesto equip the leading portion and the trailing portion of the edge ofeach of at least certain distribution orifices with an edge arrangementhaving at least one notch.

When a piston is in contact with a convex region of a ramp of the cam,it is in a bottom position, i.e. it is in the vicinity of its bottomdead center. In this situation, the volume of the working chamber of thecylinder in which the piston moves is at its minimum.

Conversely, when the piston is in contact with the concave region of theramp of the cam, it is in the vicinity of its top dead center and thevolume of the working chamber of the cylinder in which the piston movesis at its maximum.

With the invention, when a piston is in the vicinity of its bottom deadcenter, the communication orifice of the cylinder of said piston leavesthe trailing portion of a distribution orifice or enters intocommunication with the leading portion of the next distribution orificevia an edge arrangement having at least one notch suitable for passing asmall pressure-compensating volume of fluid between the orifices. Whenthe same piston is in the vicinity of its top dead center, thecommunication orifice of the cylinder of said piston leaves the trailingportion of a distribution orifice or enters into communication with theleading edge of the adjacent distribution orifice via an edgearrangement provided with at least one notch suitable for passing alarger volume of pressure-compensating fluid between the orifices.

Firstly, the invention makes it possible for the coupling between eachcommunication orifice and each distribution orifice to be establishedgradually, either via the notch or the notches in the edge arrangementallowing a small volume to pass through and disposed on one of the edgesof the distribution orifice, which arrangement is said to have a “smallnotch section”, or via the notch or the notches in the edge arrangementallowing a large volume to pass through and disposed on the other side,which arrangement is said to have a “large notch section”. This limitsthe above-mentioned pressure reduction phenomena.

In addition, the coupling between a communication orifice and the edgearrangement having a small notch section of a distribution orifice isestablished when the volume of the working chamber of the cylinderconnected to the communication orifice in question is at its minimum,whereas the coupling between the same communication orifice and the edgearrangement having a large notch section of a distribution orifice isestablished when the volume of the working chamber of the cylinderassociated with the same communication orifice is at its maximum.

By appropriately choosing the dimensions and the numbers of the notchesin the edge arrangements having the small notch section and in the edgearrangements having the large notch section, it is possible make thepressure compensation between the communication orifice and thedistribution orifices gradual, the extent to which the compensation isgradual being substantially the same in both of the above-mentionedsituations, when considered relative to the volume of the workingchamber.

Thus, by choosing a small notch section and a large notch section forthe respective edges of each distribution orifice, it is possible toguarantee that the communication orifices and the distribution orificesare put into communication even more uniformly. This further improvesthe flexibility of motor operation, because the phenomena of pressurereduction are avoided in the same way (in the same proportions) whetherthe pistons are in the vicinities of their top end positions or in thevicinities of their bottom end positions. Vibration and other unpleasantjolting phenomena are further limited.

In another variant, the edge arrangement of the leading portion of atleast one distribution orifice is provided with at least one notchwhich, relative to a notch in the edge arrangement of the trailingportion of said distribution orifice, is disposed at a different radialdistance from the axis of rotation.

The fact that the two notches are situated at different radial distancesfrom the axis of rotation can make it possible to form notches ofdifferent lengths. The different lengths are used to optimize thevariation in head loss in the notch while the fluid distributor and thecylinder block are rotating relative to each other. For example, if thenotch that is further from the axis of rotation and that is part of theedge arrangement having a large notch section is in communication withthe communication orifice over an angular sector that is larger than theangular sector over which the edge arrangement having the small notchsection is in communication with said orifice, this configuration makesit possible, while the fluid distributor and the cylinder block arerotating relative to each other, to guarantee that a communicationorifice communicates for a longer lapse of time with the edgearrangement having a large notch section than with the other edgearrangement. This difference in communication time is one of the factorsthat make it possible to impart more uniformity to the decompression orto the compression of the volume of fluid contained in the workingchamber of the cylinder block that communicates with the communicationorifice in question.

Thus, the lapse of time for which the notch that is further from theaxis of rotation and that is provided in the edge arrangement having thelarge notch section communicates with a communication orifice isgenerally longer because, for a given angle of relative rotation betweenthe cylinder block and the distributor, the distance over which a pointremote from the axis of rotation has to travel is longer than thedistance that is traveled by a point that is closer to the axis.

Another use of the length of the notch consists, for a long notch, inlimiting the communication between said notch and a communicationorifice to a small portion only of the length of the notch (i.e. over asmall angular sector of relative rotation between the cylinder block andthe distributor), before fully-fledged communication is established withthe edge itself of the distribution orifice. In which case, the longnotch constitutes a constriction of long length which passes, over thesmall portion in question, only a small pressure-compensating volume offluid. The long notch thus corresponds to the above-defined small notchsection. The notch in the other edge of the distribution orifice,disposed at a shorter radial distance from the axis of rotation, has ashorter length but it is used over its entire length over an angularsector substantially identical to the angular sector of the limitedcommunication between the long notch and the communication orificebefore fully-fledged communication is established with the edge itselfof the distribution orifice. The short notch thus passes a largerpressure-compensating volume and corresponds to the above-defined largenotch section.

In which case, advantageously, for the edge arrangements of at least onedistribution orifice, the distance from a short notch to the axis ofrotation is smaller than the distance from a long notch to the axis ofrotation.

Advantageously, for at least one distribution orifice, the edgearrangement that is disposed in angular correspondence with the concaveregion of the cam ramp corresponding to the distribution orifice inquestion is provided with at least one notch which extends over anangular sector, as measured between two radii extending from the axis ofrotation, that is larger than the angular sector, as measured in thesame way, over which the notch which is disposed in angularcorrespondence with the convex region of the ramp extends.

Advantageously, for at least one distribution orifice, the edgearrangement which is disposed in angular correspondence with the concaveregion of the cam ramp corresponding to said orifice has a notch sectionthat is larger than the notch section of the edge arrangement that isdisposed in angular correspondence with the convex region of the ramp.

In one embodiment, each of the edge arrangements of at least onedistribution orifice has the same number of notches (advantageously asinglesnotch), the notch or notches in one of the edge arrangementsbeing different from the notch or notches in the other edge arrangement.

In another embodiment, each of the edge arrangements of at least onedistribution orifice has a similar notch or similar notches, the numberof notches in one of the edge arrangements being different from thenumber of notches in the other edge arrangement.

The term “similar notches” is used to mean notches that havesubstantially the same section and that can be formed using the sametool. For example, two similar notches respectively present on theleading portion and on the trailing portion of a distribution orifice,are such that the image of one of said notches obtained by symmetryabout a plane of symmetry of the distribution orifice has a shape thatis identical or almost identical to the shape of the other notch.

It is thus possible to use the same tool to machine all of the notchesand to choose the number of notches on each edge such as to enable thedesired pressure-compensating volume to pass through them.

An advantageous variant is defined by the fact that two adjacent rampsof the cam are connected together either via a cam crest zone extendingbetween their respective convex regions, or via a cam trough zoneextending between their respective concave regions, and said cam crestzone and said cam trough zone are substantially circular arcs centeredon the axis of rotation, so that when the pistons are co-operating withsaid zones, their radial strokes are substantially zero, and by the factthat the distribution orifices and the communication orifices havedimensions such that, while the cylinder block and the distributor arerotating relative to each other, each distribution orifice remainsmomentarily isolated from any communication orifice.

The cam crest zones and the cam trough zones can be referred to as “camflats”. Advantageously, the substantially zero stroke of a piston thatco-operates with a cam flat is caused to coincide with the communicationorifice of the cylinder of said piston being isolated from anydistribution orifice. It is thus possible to avoid any significantcompression or decompression of fluid in the working chamber of thecylinder block whose piston is in contact with a cam crest zone or a camtrough zone.

The invention will be well understood and its advantages will appearmore clearly on reading the following detailed description of anembodiment shown by way of non-limiting example. The description refersto the accompanying drawings, in which:

FIG. 1 is an axial section view of a hydraulic motor whose distributionorifices can be made to be in accordance with the invention;

FIG. 2 is a cross-section view on line II—II of FIG. 1;

FIG. 3 is a fragmentary section view on the circular arc designated byIII—III in FIG. 2;

FIG. 4 shows the relative positions of a communication orifice and of adistribution orifice, while the cylinder block and the distributor arerotating relative to each other, and FIG. 4 also shows how thedistribution orifice is disposed relative to a ramp of a cam lobe;

FIG. 5 shows, in a variant, a communication orifice disposed between twodistribution orifices while the cylinder block an the distributor arerotating relative to each other; and

FIGS. 6 to 10 are variants, each of which shows a distribution orificedisposed between two communication orifices, while the cylinder blockand the distributor are rotating relative to each other.

FIG. 1 shows a hydraulic motor comprising a fixed casing in threeportions 2A, 2B, and 2C, assembled together by bolts 3.

Naturally, the invention is not limited to hydraulic motors having fixedcasings, but rather it is also applicable to hydraulic motors havingrotary casings and that are well known to the person skilled in the art.

The portion 2C of the casing is closed axially by a radial plate 2D thatis also fixed by bolts. An undulating reaction cam 4 is formed on theportion 2B of the casing.

The motor includes a cylinder block 6 which is mounted to rotate aboutan axis of rotation 10 relative to the cam 4, and which comprises aplurality of radial cylinders which are suitable for being fed withfluid under pressure, and inside which the radial pistons 14 areslidably mounted.

The cylinder block 6 rotates a shaft 5 which co-operates with it viafluting 7. The shaft carries an outlet flange 9.

The motor also includes an internal fluid distributor 16 which issecured to the casing so that it is prevented from rotating relativethereto about the axis 10. Between the distributor 16 and the insideaxial face of the portion 2C of the casing, distribution grooves areformed, namely a first groove 18, a second groove 19, and a third groove20. The distribution ducts of the distributor 16 are organized in afirst group of ducts which, like the duct 21, are all connected to thegroove 18, a second group of ducts (not shown) which are connected tothe groove 19, and a third group of ducts which, like the duct 22, areconnected to the groove 20. The first groove 18 is connected to a firstmain duct 24 to which all of the distribution orifices of thedistribution ducts of the first group, such as the orifice 21A, areconnected. The third groove 20 is connected to a second main duct 26 towhich all of the distribution orifices of the ducts of the third group,such as the orifice 22A of the duct 22, are connected.

Depending on the direction of rotation of the motor, the main ducts 24and 26 are respectively a fluid exhaust duct and a fluid feed duct, orvice versa.

The distribution ducts open out in a distribution face 28 of thedistributor 16, which face is in abutment against a communication face30 of the cylinder block. Each cylinder 12 has a cylinder duct 32 thatopens out in said communication face so that, while the cylinder blockand the cam are rotating relative to each other, the cylinder ducts comeinto communication in alternation with the distribution ducts of thevarious groups.

The motor of FIG. 1 also includes a cubic capacity selector devicewhich, in this example, comprises a bore 40 that extends axially in theportion 2C of the casing and in which an axially-movable selector slide42 is disposed. The bore 40 is provided with three communication ports,respectively 44, 46, and 48, which are connected to respective ones ofthe grooves 18, 19, and 20, via connection ducts, respectively 44′, 46′,and 48′. The slide 42 is mounted to move between two end positionsinside the bore 40, in which positions it causes the ports 44 and 46 orthe ports 46 and 48 to communicate via its groove 43.

For example, as shown in FIG. 2, the distribution orifices, asconsidered in succession in the direction in which the cylinder blockand the distributor are rotating relative to each other, comprise onepair of orifices 21A, 23A connected to respective ones of the grooves 18and 19, and one pair of orifices 21A, 22A connected to respective onesof the grooves 18 and 20. When the selector 42 is in the position shownin FIG. 1, the grooves 19 and 20 both communicate with the fluid feed.It can be understood that, while the cylinder block and the distributorare rotating relative to each other, a communication orifice 32A issuccessively connected to the high pressure and to the low pressure bycommunicating with the orifices of the two above-mentioned pairs. Whenthe selector 42 is moved in the direction indicated by arrow F so as tocause the grooves 18 and 19 to communicate with each other, then the twodistribution orifices 21A, 23A of the first above-mentioned pair areboth connected to the same pressure. Said pair is thus inactivatedbecause, when a communication orifice goes from one to the other of thetwo distribution orifices of said pair, the pressure in the cylinderduct connected to said communication orifice does not change.Conversely, the next pair is active because a communication orificecommunicating respectively with the two orifices 21A, 22A of said pairis placed successively at the high pressure and at the low pressure.

The situation shown in FIG. 1 is thus a large cubic capacity situation,whereas the situation in which the selector 42 is moved in the directionindicated by arrow F in order to put the grooves 18 and 19 intocommunication with each other is a small cubic capacity situation. Insuch a situation, the pairs of orifices 21A and 23A are inactive, whilethe pairs of orifices 21A and 22A are active.

When the cylinder block moves relative to the distributor in thedirection of rotation R1 indicated in FIG. 2, the portions B1 of theedges of the distribution orifices constitute leading portions, viawhich a communication orifice starts being put into communication with adistribution orifice, while the portions B2 of the edges of thedistribution orifices constitute trailing portions, via which thecommunication ceases. Naturally, when the relative rotation takes placein the opposite direction R2, it is the portions B2 that constitute theleading portions and the portions B1 that constitute the trailingportions.

In the embodiment shown in FIG. 2, each of the leading portions B1 andof the trailing portions B2 of each distribution orifice (considered inthe direction of rotation R1) is provided with an edge arrangementprovided with a notch. It can be seen that the notches are of differentsizes, the notches 54A of the edge arrangement 53A of the edges B1 ofthe distribution orifices 23A and 22A, and the notches 54A of the edgearrangements 53A of the edges B2 of the orifices 21A being smallnotches, these edges thus having small notch sections, whereas thenotches 54B of the edge arrangements 53B of the edge B2 of thedistribution orifices 23A and 22A, and the notches 54B of the edgearrangements 53B of the edges B1 of the orifices 21A are large notches,these edges thus having large notch sections.

Insofar as the cam and the distributor are constrained to rotate witheach other, the position of each distribution orifice relative to thelobes of the cam is fixed.

Each lobe of the cam is provided with two ramps, each of which has aconvex region and a concave region. FIG. 4 shows one of the ramps 50,whose convex region, closer to the axis of rotation 10, is designated byreference 51, and whose concave region, further away from the axis, isdesignated by reference 52. A cam lobe is constituted by said ramp 50,and by another ramp symmetrical to the ramp 50 about the radius Rpassing through the axis of rotation of the motor. The adjacent cam lobeis provided with a ramp 50′ symmetrical to the ramp 50 about the radiusRS.

A distribution orifice is associated with each ramp of the cam. Eachdistribution orifice is thus angularly corresponds to a respective rampof the cam. Although the distribution orifices are not in the sameradial plane as the cam, FIG. 4 shows how a distribution orifice 23Aangularly corresponds to the ramp 50 of the cam. In addition, in orderto make the drawing clearer, it is out of proportion, with thecommunication and distribution orifices being shown closer to the camthan they really are. Substantially, the orifice 23A is disposed so thatthe circle within which it lies and which passes through the ends of thenotches is substantially symmetrical about a radius RC of the cam, whichradius intersects said cam substantially in a zone of inflection betweenits convex region 51 and its concave region 52.

FIG. 4 shows that the notch 54A in the portion B1 of the edge of theorifice 23A is a small notch, whereas the notch 54B in the portion B2 ofthe edge of the orifice 23A is a large notch. The small notch 54A is inangular correspondence with the convex potion 51 of the cam, i.e. aradius of the cam extending radially from the axis of rotation 10 of themotor and passing through the notch 54A intersects the ramp 50 in theconvex region 51 thereof. The notch 54B is in angular correspondencewith the concave region 52 of the ramp 50, i.e. a radius of the camextending from the axis of rotation 10 and passing through the notch 54Bintersects the ramp 50 in the concave region thereof.

FIG. 4 also shows the various positions of a communication orificerelative to the distribution orifice 23A while the cylinder block andthe distributor are turning relative to each other. For example, it isconsidered that the cylinder block turns in the direction R2 relative tothe cam, in which direction the portions B2 and B1 of the edge of theorifice 23A constitute respectively the leading portion and the trailingportion.

Firstly, a position 32A1 of the communication orifice 32A exists inwhich said communication orifice is isolated from any distributionorifice. It can be seen that, in this position, the orifice 32A isseparated from the tip of the notch 54B of the orifice 23A by an angulardistance α1, e.g. about 1°, and it is also isolated from the notch 54Bin the preceding distribution orifice 21A. When the cylinder block turnsrelative to the distributor in the direction R2, the communicationorifice gradually comes to cover the notch 54B in the orifice 23A and,over an angular displacement α2, e.g. through about 2°, it communicateswith the distribution orifice 23A via said notch 54B only, until ittakes up a position 32A2.

When the cylinder block continues to turn relative to the distributor inthe direction R2, the communication orifice gradually covers the entireorifice 23A, and a positions 32A3 exists in which the distributionorifice 23A is totally covered by the communication orifice, thecommunication section via which the distribution orifice communicateswith the communication orifice then being at its maximum.

When the cylinder block continues to turn relative to the distributor inthe direction R2, the communication section decreases, and thecommunication orifice reaches a position 32A4 in which it communicateswith the distribution orifice 23A only via the notch 54A in the edge ofsaid orifice. It then remains for it to travel over an angular strokeα3, e.g. of about 1°, for communication with the distribution orifice23A to cease totally. It then remains for the communication orifice totravel over an angular stroke α4, e.g. of about 1°, before it starts tocommunicate with the distribution orifice 21A that is situated after thedistribution orifice 23A in the direction of rotation R2, via the notch54A in said orifice 21A.

For the large notch 54B, when the communication orifice occupies itsposition 32A2, the total section of the communication passageway betweensaid orifice and the distribution orifice 23A is larger than the sectionof the communication passageway which is established, via the smallnotch 54A, between the same distribution orifice and the communicationorifice when it occupies its position 32A4.

The ratio between said sections is advantageously chosen as a functionof the ratio between the volumes of the working chamber of the cylinder12 fed via the communication orifice 32A in question when saidcommunication orifice occupies respectively its position 32A2 and itsposition 32A4.

For example, the ratio between the communication sections permitted bythe notches 54B and 54A is proportional to the ratio between the volumeof the working chamber of the cylinder fed via the orifice 32A when saidorifice is in its position 32A2 and the volume of the same workingchamber when the orifice 32A is in its position 32A4.

It can be observed that the large notch 54B extends over an angularsector α2, measured between two radii extending from the axis of themotor, that is larger than the angular sector α3 (also measured betweentwo radii extending from the axis of the motor) over which the smallnotch 54A extends.

The ramp 50 of the cam is connected to the adjacent ramp 50′ via a camcrest zone 56 which extends between the convex region 51 of the ramp 50and the convex region of the ramp 50′, and it is connected to the otherramp that is adjacent to it, namely ramp 50″, via a cam trough zone 58which extends between the concave region 52 of the ramp 50 and theconcave region of the ramp 50″. The cam crest zones are the zones inwhich the radial distance from the cam to the axis of rotation is at itsminimum, whereas the cam trough zones are the zones in which the radialdistance from the cam to the axis of rotation is at its maximum.

When the orifice 32A is considered, it is observed that, between itsposition 32A1 and its position 32A2, said orifice travels over anangular displacement α1+α2 that is equal to the angle α′1 correspondingto a cam trough portion 58 situated on one side of the radius ofsymmetry R. In other words, while the cylinder block and the distributorare rotating relative to each other, when the communication orifice goesfrom its position 32A1 to its position 32A2, the piston of the cylinderfed by said communication orifice co-operates with the cam trough zone58. Over a portion of this angular path, corresponding to the angulardisplacement α1, the orifice 32A is isolated from any distributionorifice. Over the remaining portion, corresponding to the displacementα2, it is in communication with the distribution orifice 23A via thegroove 54B only.

When a piston co-operates with the cam trough zone 58, its radial strokeis zero or substantially zero. For example, it is at the mostsubstantially equal to 0.5% of the amplitude of the stroke of the pistonbetween its top dead center and its bottom dead center. For thispurpose, the cam trough zone 58 is substantially a circular arc centeredon the axis of rotation. This means that the cam trough zone is either acircular arc centered on the axis of rotation, or a region which, overthe entire angular distance 2α′1 that it covers, has a radial distanceto the axis of rotation of the motor that is substantially equal to themaximum radial distance from the cam to the axis of rotation 10. Insofaras, when the communication orifice travels over the angular travel α1,it is isolated from any distribution orifice, the pressure in theworking chamber of the cylinder fed by said orifice remainssubstantially constant during this displacement. The shape of the camtrough zone then makes it possible to avoid any significant compressionof fluid in said chamber. Over the remaining portion α2 of the stroke ofthe communication orifice 32A, during which the piston of the cylinderfed by said orifice co-operates with the cam trough zone 58, saidcommunication orifice communicates with the distribution orifice via thenotch 54B only. Advantageous use is made of said remaining portion, overwhich the piston does not have to move radially, to cause the pressurein the working chamber of the piston to vary “smoothly” by means of thecommunication established via the notch 54B. In this example, since theorifice 23A is connected to the fluid discharge, the pressure thendecreases very gradually in the working chamber, until it reaches avalue close to or equal to the pressure of the orifice 23A when thecommunication orifice has gone beyond its position 32A2 in the directionof rotation R2, in which case the piston of the cylinder fed via saidorifice co-operates with the ramp 50 and moves radially towards the axisof rotation of the motor.

The angle α′2 over which the portion of the cam crest zone 56 that issituated on one side of the radius of symmetry RS extends corresponds tothe path traveled by the communication orifice 32A between its position32A4 and its position 32A5, in which it is ready to start coming intocommunication with the distribution orifice 21A that follows the orifice23A in the direction R2, via the small notch 54A of said distributionorifice 21A. This means that the communication orifice moves between itspositions 32A4 and 32A5 while the piston of the cylinder fed via saidorifice co-operates with the cam crest zone 56. While it is moving overthe path α3, the communication orifice 32A continues to communicate withthe distribution orifice 23A, but only via the small groove 54A, andthen, over the path α4, it is isolated from any distribution orifice.The cam crest zone 56 substantially defines a circular arc centered onthe axis of rotation. It can either really form such a circular arc, orelse have, over the entire angular distance 2α2 that it covers, a radialdistance to the axis of rotation of the motor that is substantiallyequal to the minimum radial distance from the cam to the axis ofrotation 10, while differing, for example, from said radial distance byat the most about 0.5%.

In the same way as for the cam trough zones 58, advantageous use is madeof this situation in which the piston fed via the communication orifice32A does not have to move radially to any significant extent, in orderto open “smoothly” the coupling between said orifice and the nextdistribution orifice 21A.

FIG. 3 shows the position of a communication orifice 32A between twodistribution orifices 23A and 21A. It can be seen that the notches 54Bare longer than the notches 54A, i.e. they extend over angular travelsα2 (see FIG. 4) that are larger than the angular travels (α3) over whichthe notches 54A extend. The notches 54B are also slightly deeper thanthe notches 54A.

In order to form the notches, it is possible to start from an orificethat is exactly circular and to apply a milling cutter that extends in adiametrical plane of said orifice, and that is moved axially relativethereto. If the milling cutter is circular, with a diameter slightlyoffset relative to the axis of the orifice in question, it is thuspossible to make the notches 54B longer and deeper than the notches 54A.

In the above-described figures, the distribution orifices are circular,except for the notches 54A and 54B. It is however possible to choosedistribution orifices of different shapes. Thus, FIG. 5 shows acommunication orifice 32A which is circular, disposed between twodistribution orifices, respectively 123A and 121A, which arenon-circular. For said distribution orifices, both the leading portion(B2, if the cylinder block is turning in the direction R2 relative tothe distributor and B1, if the direction of relative rotation is R1),and also the trailing portion (B1 if the relative rotation direction isR2 and B2 if the relative rotation direction is R1) are substantiallyconvex, as seen from the inside of the orifice. Substantially, exceptfor the edge arrangements 53′A and 53′B which are provided with theabove-described notches 54A and 54B, the leading portions and thetrailing portions form circular arcs which, when the distributor and thecylinder block are moving relative to each other, come to overlap theedge of a communication orifice, when said communication orificeoccupies a position corresponding to the position 32A2 or to theposition 32A4 shown in FIG. 4.

Thus, the distribution orifices substantially have the shapes describedin Patent Application FR-A-2 587 761.

This configuration makes it possible, once communication has beenestablished via the notches 54A or 54B, and when the relative rotationbetween the distributor and the cylinder block continues, to increasevery rapidly the communication section over which the distributionorifices and the communication orifices communicate. Thus, by means ofthe notches, the above-mentioned jolting effects are avoided, but, bymeans of the particular shape of these distribution orifices, it is thenpossible for communication to be established very fast so that theefficiency of the motor is improved.

In FIG. 5, the communication orifice 32A has a substantially circularcross-section, and the above-mentioned convex shape of the edges of thedistribution orifices 121A and 123A is the shape that makes it possibleto increase fastest the communication between the communication orificeand the distribution orifices, after initial communication has beenestablished via the notches 54A and 54B.

In general, it is advantageous for the leading portions and for thetrailing portions of the distribution orifices to have shapes that aresubstantially complementary to the shapes of the edges of thecommunication orifices via which the communication between thedistribution orifices and the communication orifices opens or closes.

FIG. 6 shows a distribution orifice 221A disposed, while the cylinderblock and the distributor are rotating relative to each other, betweentwo communication orifices, respectively 32A and 32′A, while beingsimultaneously isolated from said two orifices.

In order to make the drawing clearer, FIG. 6 shows the circular arcs C1and C2 between which the communication and distribution orifices aredefined. If the direction in which the cylinder block and thedistributor are turning relative to each other is such that the cylinderblock turns in the direction R1 relative to the distributor, then thenotch 254A is disposed on the leading portion B1 of the edge of thedistribution orifice 221A, whereas the notch 254B is disposed on thetrailing portion B2 of the edge of said orifice. It can be seen that thenotches 254A and 254B of the edge arrangements 253A and 253B aredisposed at different radial distances from the axis of rotation.

More precisely, the distance from the small notch 254A to the axis ofrotation of the motor is smaller than the distance from the large notch254B to said axis, and the angular sector over which the large notchlimits the communication between the orifices is larger than the angularsector of the small notch. While the cylinder block and the distributorare rotating relative to each other, this makes it possible to ensurethat the lapse of time for which the distribution orifice 211Acommunicates with the communication orifice 32A via the notch 254B onlyis longer than the lapse of time for which the distribution orificecommunicates with the communication orifice 32′A via the notch 254Aonly. In addition, the length of the notch 254B, as measuredtangentially relative to the axis of rotation of the motor, is longerthan the length of the notch 254A.

In the example shown in FIG. 6, both of the notches 254A and 254′B havesubstantially the same thickness e, as measured along a radius passingthrough the axis of rotation of the motor.

FIG. 7 differs from FIG. 6 only in that the notch 254′B of the trailingportion B2 of the distribution orifice 221A is slightly different fromthe notch 254B. The notch 254′B in the edge arrangement 253′B has amaximum thickness e1, as measured along a radius passing through theaxis of rotation, that is greater than the thickness e, also as measuredalong a radius passing through the axis of rotation, of the notch 254Ain the edge arrangement 253A. For example, the thickness e1 issubstantially equal to twice the thickness e. Thus, the large notch254′B forms an opening that is larger than the small notch 254A.

In FIGS. 6 and 7, the distribution orifice 221A is oblong, its largestdimension being measured along a radius passing through the axis ofrotation.

In FIG. 8, and considering that the cylinder block is turning in thedirection R1 relative to the cam, the distribution orifice 321A has atrailing portion B2 whose edge arrangement 354A is provided with a notch354B of section greater than the section of the notch 354A of the edgearrangement 353A of the leading portion B1. The trailing portion B2 ofthe distribution orifice is substantially in the shape of an arc of acircle whose center is situated inside said orifice.

For example, the notch 354A is analogous to the notch 254A of FIGS. 6and 7. The leading portion B1 has a shape substantially complementary tothe shape of the edge C of the communication orifice 32′A via whichcommunication between the communication orifice and the distributionorifice opens when the cylinder block turns in the direction of rotationR1 relative to the distributor. It is also via said edge C that thecommunication between the distribution orifice and the communicationorifice 32′A closes when the cylinder block turns relative to thedistributor in the direction R2 opposite from direction R1. The leadingportion B1 is convex, when it is considered from the inside of thedistribution orifice 321A. It is substantially in the shape of acircular arc suitable for covering the circular arc formed by theportion C1 of the communication orifice 32′A. Thus, in the direction ofrotation R1, communication between the distribution orifice 321A and thecommunication orifice 32′A takes place firstly via a very small section,due to the notch 354A, and then it increases very quickly because of theshape of the leading portion B1.

In the opposite direction of rotation R2, it is observed that, becauseof the shape of the edge B2, only a portion of the notch 354B makescommunication possible via a limited section between the orifices 321Aand 32A before fully-fledged communication is established between theorifices. The section of this portion of the notch 354B is larger thanthe section of the notch 354A.

Naturally, it is possible to equip distribution orifices substantiallyhaving the same shape as the orifice 321A with notches analogous to anyof the above-mentioned notches 54A, 54B, or 254A, 254B.

In FIG. 9, the distribution orifice 421A is substantially circular inshape except for its notches. It can be seen that the notches 454A inthe edge arrangement 453A of its leading portion B1 and 454B of the edgearrangement 453B of its trailing portion B2 (in the direction ofrotation R1) are situated at different radial distances from the axis ofrotation of the motor. In FIGS. 6 to 8, the small notch 254A or 354A issituated substantially on an arc of a circle centered on the axis ofrotation of the motor and passing through the geometrical centers of thecommunication orifices 32A and 32′A, whereas the large notch 254B, 254′Bor 354B is situated beyond said arc of a circle, going away from theaxis of rotation.

In FIG. 9, the “small” notch 454A is the notch that is longer and it issituated beyond a circular arc A passing through the geometrical centersof the communication orifices 32A and 32′A and centered on the axis ofrotation, whereas the “large” notch 454B is the notch that is shorterand it is situated within said circular arc. The notes 454A and 454Bhave identical sections.

Disposing the longer notch 454A in this way makes it possible to limitthe volume of fluid passing through the notch over the small portion ofits length in communication with the communication orifice, before thefully-fledged communication is established with the edge itself of thedistribution orifice. This limiting of the volume is due to the headloss generated by the long length of constriction formed by said notch.The shorter notch 454B is used over its entire length over the sameangular sector centered on the axis of rotation as the angular sector ofthe limited communication between the long notch 454A and thecommunication orifice before fully-fledged communication is establishedwith the edge itself of the distribution orifice. The notch 454B thusallows a larger pressure-compensating volume through.

The advantage of this configuration is that it is possible to keep thecircular distribution and communication orifices of standarddistributors (without notches) and to form the notches defined for eachapplication as a function of the working pressures, of the rotationspeeds, and of the volumes of the working chambers at the top and bottomdead centers.

In the example that has just been described, the edges of all of thedistribution orifices are provided with notches, respectively on theleading portions and on the trailing portions.

In addition, as can be seen in FIG. 2, all of the large notches 54B havethe same size, while all of the small notches 54A have the same size.

It is possible for only certain distribution orifices to have theiredges provided with notches or else for certain distribution orifices tohave notches having given dimensions that are smaller than thedimensions of the notches of the other distribution orifices.

In particular, in the description of FIGS. 1 and 2, it is indicated thatthe motor shown has two active operating cubic capacities, i.e. a largecubic capacity in which each pair of consecutive distribution orifices(21A, 23A; 21A, 22A) comprises one orifice (22A or 23A) connected to thefluid feed and one orifice (21A) connected to the fluid exhaust. For themotor of FIG. 1, the large cubic capacity is obtained when the selector42 is in the position shown.

The motor also has a small active operating cubic capacity in whichcertain pairs of consecutive distribution orifices (21A, 22A) are activeand in which each of them comprises one orifice (22A) connected to thefluid feed and one orifice (21A) connected to the fluid discharge, whileother pairs of distribution orifices (21A, 23A) are inactive and each ofthem has both of its orifices connected to the same pressure.

When the motor is operating in the small active operating cubiccapacity, and with the feed fluid flow-rate remaining the same, itsspeed is higher than when it operates in its large cubic capacity.However, it delivers lower torque when in its small cubic capacity.

The above-mentioned jolting or knocking phenomena are even moreperceptible when the motor operates at high speed. For this reason, itis possible to make provision for only the edges of the distributionorifices of the pairs active when in the small cubic capacity to beprovided with edge arrangements having notches. As described above, thenotches then comprise small notches of the type of the notches 54A andlarge notches of the type of the notches 54B, depending on theirrespective positions relative to the convex and the concave regions ofeach cam ramp.

In an alternative manner, it is possible to make provision for the edgesof the distribution orifices of the pairs that are active when in thesmall cubic capacity to have edge arrangements having notch sectionsthat are larger than those of the edge arrangements of the distributionorifices of the pairs that are inactive when in the small cubiccapacity. Thus, the edge arrangements of the distribution orifices ofthe pairs that are active in the small cubic capacity comprise one smallnotch and one large notch respectively disposed in angularcorrespondence with a convex zone and with a concave zone of the cam,whereas the edge arrangements of the orifices of the pairs that areinactive in the small cubic capacity also comprise one small notch andone large notch respectively situated facing a convex zone and concavezone of the cam, but said notches of the orifices that are inactive inthe small cubic capacity are smaller than the notches of the orificesthat are active in the small cubic capacity.

In the figures described above, each edge arrangement of a distributionorifice has a single notch and the small or large notch sections areobtained by choosing a small or a large notch.

In FIG. 10, the edge arrangements 553A and 553B of the distributionorifice 521A are provided with different numbers of similar notches. Theedge arrangement 553A is thus provided with a notch 554A, whereas theedge arrangement 553B is provided with two notches 554B and 554′B.

The single notch 554A thus defines, for the arrangement 553A, a notchsection that is smaller than the notch section that is defined by thetwo notches 554B and 554′B for the arrangement 553B.

These notches can be formed using the same tool that is displacedappropriately relative to the orifice 521A.

1. A hydraulic motor having radial pistons; and comprising a cam and acylinder block that are suitable for turning relative to each otherabout an axis of rotation, the cylinder block having radial cylindersconnected via cylinder ducts to communication orifices situated in acommunication face of the cylinder block that is perpendicular to theaxis of rotation, pistons mounted to slide in the cylinders beingsuitable for co-operating with the cam, which cam is provided with aplurality of lobes, each of which has two ramps, each of which has aconvex region and a concave region, the motor further comprising a fluiddistributor having a distribution face that is perpendicular to the axisof rotation and that is suitable for being in abutment against thecommunication face of the cylinder block, said distribution face beingprovided with distribution orifices comprising orifices suitable forbeing connected to a fluid feed and orifices suitable for beingconnected to a fluid discharge, the fluid distributor being constrainedto rotate with the cam, so that there is one ramp of the cam thatcorresponds to each distribution orifice, said distribution orificesbeing suitable for communicating one after another with thecommunication orifices while the cylinder block and the distributor areturning relative to each other, the edge of each distribution orificehaving a leading portion via which communication between thedistribution orifice and the communication orifices opens while thecylinder block and the distributor are turning relative to each other ina given direction of relative rotation, and a trailing portion via whichcommunication between the distribution orifice and the communicationorifices closes while the cylinder block and the distributor are turningrelative to each other in said given direction of relative rotation,each leading portion and each trailing portion of the edges of at leastcertain distribution orifices having an edge arrangement provided withat least one notch, said edge arrangements of a distribution orificebeing different, the edge arrangement of a distribution orifice which isdisposed in angular correspondence with the convex region of the ramp ofthe cam corresponding to the distribution orifice in question beingsuitable for allowing a pressure-compensating volume of fluid to passthrough between a communication orifice and the distribution orificethat is smaller than the pressure-compensating volume of fluid that isallowed to pass by the edge arrangement of the same distribution orificethat is disposed in angular correspondence with the concave region ofsaid ramp.
 2. A motor according to claim 1, wherein for at least certaindistribution orifices, the leading portion and the trailing portion haveshapes that are substantially complementary to shapes of the edges ofthe communication orifices via which the communication between thedistribution orifices and the communication orifices open.
 3. A motoraccording to claim 2, wherein for each distribution orifice, the leadingportion and the trailing portion are substantially convex, as seen fromthe inside of the orifice.
 4. A hydraulic motor according to claim 1,wherein the edge arrangement of the leading portion of at least onedistribution orifice is provided with at least one notch which, relativeto a notch in the edge arrangement of the trailing portion of the edgeof said distribution orifice is disposed at a different radial distancefrom the axis of rotation.
 5. A motor according to claim 4, wherein forthe edge arrangements of at least one distribution orifice, the distancefrom a short notch to the axis of rotation is smaller than the distancefrom a long notch to the axis of rotation.
 6. A motor according to claim1, wherein for at least one distribution orifice, the edge arrangementthat is disposed in angular correspondence with the concave region ofthe ramp is provided with at least one notch which extends over anangular sector, as measured between two radii extending from the axis ofrotation, that is larger than an angular sector, as measured in the sameway, over which the notch which is disposed in angular correspondencewith the convex region of said ramp extends.
 7. A motor according toclaim 1, wherein for at least one distribution orifice, the edgearrangement which is disposed in angular correspondence with the concaveregion of the ramp has a notch section that is larger than the notchsection of the edge arrangement that is disposed in angularcorrespondence with the convex region of said ramp.
 8. A motor accordingto claim 1, wherein each of the edge arrangements of at least onedistribution orifice has the same number of notches, the notch ornotches in one of the edge arrangements being different from the notchor notches in the other edge arrangement.
 9. A motor according to claim1, wherein each of the edge arrangements of at least one distributionorifice has a similar notch or similar notches, the number of notches inone of the edge arrangements being different from the number of notchesin the other edge arrangement.
 10. A motor according to claim 1, whereintwo adjacent ramps of the cam are connected together either via a camcrest zone extending between their respective convex regions, or via acam trough zone extending between their respective concave regions, saidcam crest zone and said cam trough zone being substantially circulararcs centered on the axis of rotation, so that when the pistons areco-operating with said zones, radial strokes thereof are substantiallyzero, and the distribution orifices and the communication orificeshaving dimensions such that, while the cylinder block and thedistributor are rotating relative to each other, each distributionorifice remains momentarily isolated from any communication orifice. 11.A motor according to claim 10, wherein the cam crest zones extend overangular sectors, as each measured between two radii extending from theaxis of rotation, that are smaller than angular sectors, as measured inthe same way, over which the cam trough zones extend.
 12. A motoraccording to claim 1, having two active operating cubic capacities,namely a large cubic capacity in which each pair of consecutivedistribution orifices comprises one orifice connected to the fluid feed,and one orifice connected to the fluid discharge, and a small cubiccapacity in which certain pairs of consecutive distribution orifices areactive and each of them comprises one orifice connected to the fluidfeed and one orifice connected to the fluid discharge, whereas otherpairs of distribution orifices are inactive and each of them comprisestwo orifices connected to the same pressure, only the edges of thedistribution orifices of the pairs that are active in the small cubiccapacity being provided with notches.
 13. A motor according to claim 1,having two active operating cubic capacities, namely a large cubiccapacity in which each pair of consecutive distribution orificescomprises one orifice connected to the fluid feed and one orificeconnected to the fluid discharge, and a small cubic capacity in whichcertain pairs of consecutive distribution orifices are active, and eachof them comprises one orifice connected to the fluid feed and oneorifice connected to the fluid discharge, whereas other pairs ofdistribution orifices are inactive, and each of them comprises twoorifices connected to the same pressure, the edges of the distributionorifices of the pairs that are active in the small cubic capacity havingedge arrangements that have notch sections that are larger than notchsections of the edge arrangements of the distribution orifice that areinactive in the small cubic capacity.